Playframework 2.2.X scala - 我如何在 json 的写入中使用隐式变量

Question

我使用 Play 2.2 json 写入助手：http://www.playframework.com/documentation/2.2.x/ScalaJson

我想写一个 json 版本的 File case 类。这是我的作者：

implicit val fileWrites = new Writes[File] {
def writes(file: File) = Json.obj(
  "name" -> file.name,
  "description" -> file.description,
  "contentType" -> file.contentType,
  "lastModify" -> file.lastModify,
  "size" -> file.size,
  "link" -> routes.Document.downloadFromPermalink(file.uuid).absoluteURL(false)
  )
}

但是，这个routes.Document.downloadFromPermalink(file.uuid).absoluteURL(false) 需要一个implicit request: RequestHeader。如果我将 fileWrites 定义放在具有隐式请求范围的操作中，它就可以工作。

但我想将 fileWrites 定义为可在操作之间重用。我该如何编写它以便 fileWrites 将隐式请求作为参数？

这个定义也有同样的问题：

implicit val fileWrites: Writes[File] = (
  (JsPath \ "name").write[String] and
  (JsPath \ "description").write[Option[String]] and
  (JsPath \ "contentType").write[String] and
  (JsPath \ "lastModify").write[Date] and
  (JsPath \ "size").write[Long] and
  (JsPath \ "link").write[String])
(f => (f.name, f.description, f.contentType, f.lastModify, f.size, routes.Document.downloadFromPermalink(f.uuid).absoluteURL(false)))

编辑wingedsubmariner的答案：

它不适用于范围内的请求：

  def documents(id: Long) = Action { implicit request =>
    Users.findById(id).map { user =>

      //get files from somewhere
      val files = XXX

      //it works if I put fileWrites here but I want a reusable function

      //error on this line : No Json deserializer found for type List[models.File]. Try to implement an implicit Writes or Format for this type.
      val json = Json.toJson(files)
      Ok(json)
    }.getOrElse(NotFound)
  }

  implicit def fileWrites(implicit request: RequestHeader) = new Writes[File] {
    def writes(file: File) = Json.obj(
      "name" -> file.name,
      "description" -> file.description,
      "contentType" -> file.contentType,
      "lastModify" -> file.lastModify,
      "size" -> file.size,
      "link" -> routes.Document.downloadFromPermalink(file.uuid).absoluteURL(false))
  }

Answer 1

试试：

implicit def fileWrites(implicit request: RequestHeader) = new Writes[File] {
  def writes(file: File) = Json.obj(
    "name" -> file.name,
    "description" -> file.description,
    "contentType" -> file.contentType,
    "lastModify" -> file.lastModify,
    "size" -> file.size,
    "link" -> routes.Document.downloadFromPermalink(file.uuid).absoluteURL(false)
  )
}